1. Field of the Invention
This invention relates to integrated circuit (IC) packages, and more particularly, to a BGA (Ball-Grid Array) IC package with an unembedded type of heat-dissipation structure.
2. Description of Related Art
The BGA IC packaging technology allows an IC package to be made very small in size while nevertheless providing highly integrated functionality from a single IC package. During the operation of the IC chip, however, a large amount of heat would be generated from the internal circuitry of the IC chip. Therefore, it is required to provide heat-dissipating means on the IC package for heat dissipation during operation. To allow a BGA IC package to dissipate the IC-produced heat during operation, a conventional solution is to arrange a heat sink or a heat slug in the package structure.
The U.S. Pat. No. 5,285,352 discloses a BGA IC package configuration that utilizes a heat sink for heat dissipation, whose structure is illustrated in FIG. 4. As shown, the BGA IC package configuration 110 includes an IC chip 112 mounted on a substrate 114 by means of silver paste 116, and is characterized in that a heat sink 128 is embedded in an opening 130 formed in the substrate 114 and beneath the IC chip 112. The heat sink 128 has a top side abutted on the bottom side of the IC chip 112 and a bottom side exposed to the atmosphere from the bottom side of the substrate 114. The IC-produced heat during operation can be dissipated through this heat sink 128 to the outside of the package body.
Moreover, the U.S. Pat. No. 5,642,261 discloses a BGA IC package configuration that utilizes a heat slug for heat dissipation, whose structure is illustrated in FIG. 5. As shown, the BGA IC package configuration includes an IC chip 70 mounted on a substrate 74, and is characterized in that a heat slug 72 is arranged beneath the IC chip 70. The heat slug 72 has a top side abutted on the bottom side of the IC chip 70 and a bottom side exposed to the atmosphere from the bottom side of the substrate 74. The IC-produced heat during operation can be dissipated through this heat slug 72 to the outside of the package body.
In addition, the U.S. Pat. No. 5,583,377 discloses a BGA IC package configuration that utilizes a heat sink for heat dissipation, whose structure is illustrated in FIG. 6. As shown, the BGA IC package configuration includes an IC chip 213 and a substrate 212, and is characterized in the use of a heat sink 222 having a base portion 224, a sidewall portion 226, and a flange portion 228. The heat sink 222 is embedded in an opening 220 formed in the substrate 212, and its flange portion 228 is fixed on the rim of the opening 220 on the top surface of the substrate 212. The IC chip 213 is mounted by means of silver paste 230 on the base portion 224 within the space defined by the sidewall portion 226. The IC-produced heat during operation can be dissipated through this heat sink 222 to the outside of the package body.
The foregoing patented package structures, however, have the following draw-backs.
First, since the heat slug or heat sink is embedded in the substrate and is different in coefficient of thermal expansion (CTE) from the substrate, the substrate would be easily subjected to compressive stress resulted from the heat slug or heat sink when undergoing a temperature change during the molding process, and thus easily deformed or broken.
Second, since the embedding of the heat slug or heat sink in the opening of the substrate would hardly achieve absolute airtightness, it would easily allow ambient moisture to enter into the inside of the package body. If the inside of the package body contains moisture, it would easily explode during the solder reflow process, resulting in the so-called popcorn effect, which can break up the entire package body.
Third, since it is required to form an opening in the substrate, it would make the overall manufacture process more complex, thus increasing the overall manufacture cost. In addition, the making of the heat slug and heat sink would require precise machining so as to allow the heat slug or heat sink to be fitted snuggly to the opening, which is also hard to achieve, thus resulting in poor quality of the manufactured IC package.
Fourth, since the heat slug or heat sink is typically made of metal, it would considerably increase the overall weight of the entire IC package, thus undesirably making the manufactured IC package heavier to handle.